How can I get out of this unproductive rut? Wasting time on the computer, achieving NOTHING...?

I'm the same way--I can't do anything productive unless I have a deadline. Try making yourself a schedule for the week and come up with some way to reward yourself for sticking to it and getting everything done. Use the computer as your reward--don't let yourself get on the computer until you get everything done that you need to do that day, that way you can't procrastinate.